For example, in a process of forming a capacitor of a DRAM (Dynamic Random Access Memory), studies have been done to form a relatively deep concave portion in a silicon oxide (SiO2) film. To this end, there is a need to form a mask film having high etching selectivity with regard to the SiO2 film on the SiO2 film. That is, there is a need to form a mask film having high etching resistance on the SiO2 film when the SiO2 film is etched. In addition, techniques for forming a W film are known in related arts.
As the mask film, a silicon (Si) film or a Si film doped with impurities has been used. However, it has been known from evaluation on etching resistance that a W film is higher in etching resistance than the Si film and therefore studies have been done to form the W film as the mask film. However, since the W film has low adhesion to the SiO2 film, when the W film is directly formed on the SiO2 film, the W film may be peeled off, thus causing the SiO2 film to be damaged by sputtering.
In order to increase the adhesion, it is considered to form a titanium nitride (TiN) film, which serves as an adhesion layer to the SiO2 film, on the SiO2 film and form a W film using the TiN film as a base (adhesion layer). A method of forming the W film using the TiN as the base will be described in detail below. First, the TiN film is formed on a SiO2 film of a substrate, and a monosilane (SiH4) gas is supplied onto the substrate. The SiH4 gas is supplied to increase activated sites on the TiN film, promoting growth of the W film and increasing the density of the W film. Thereafter, a tungsten hexafluoride (WF6) gas and a SiH4 gas are, for example, alternately supplied to form a seeding layer (W film). Thereafter, a WF6 gas and a hydrogen (H2) gas are supplied to form the W film. The W film formed by the WF6 gas and the H2 gas has a lower resistance, fewer impurities, and a higher crystallinity than the seeding layer. In addition, it is difficult to grow the W film using the WF6 gas and the H2 gas without forming the seeding layer.
However, since the method of forming the W film using the TiN film as the base requires the supply of various gases after forming the TiN film, the number of steps in the method are increased, thus taking more time and effort. Accordingly, there is a need to save time and effort in forming the W film and provide high uniformity in thickness of the W film in a plane of the substrate and between substrates.